NERVAfan

We do have random asteroids though, so I suppose random "minor moons" around a gas giant could exist (the main moons like the ones we have now would still be the same for everybody, I mean like ARM asteroids but in an orbit around Jool/GP2 instead of around the Sun).

Why? I mean, an Orion is already built to stand up to nukes... (OK, not direct impacts, there is some distance between the explosion and the pusher plate. Still I would think an Orion coasting 'plate first' would be a lot less damaged by interstellar dust than a sail.) Unless you're saying that the sail would be full of holes but not enough to really affect its performance as a sail? Maybe. I wonder if it would stay 'deployed'/keep its shape under really energetic impacts though. Once you're talking manned interstellar missions, probably decades of closed ecological system... that's a really big sail. If you're building in space anyway, with established space industry (and you might need to for a ridiculously big sail), what's the problem with a nuclear pulse engine? There won't be much area at risk because you'll have a really thick layer of ice and/or asteroid for shielding. The ship might be a billion tons or more but there's a LOT of deuterium in the outer Solar System, so who cares? EDIT: I think sails with close sun passes might make a lot of sense for interstellar precursor missions, flybys of distant KBOs etc. Maybe even interstellar probes if they can survive the dust impacts. But I think for manned missions you need fusion.

I think they're really talking about unmanned interstellar missions. Supposedly if you use a really light sail and a very close sun flyby you can get to Alpha Centauri in a thousand years or so. Still impractically long IMO, but way better than 70 or 80 thousand with chemical propulsion. If you use a giant laser in space close to the sun (for maximum solar power) you could get them going really fast. I actually do think nuclear pulse propulsion is better since I think really light flimsy solar sails are likely to get shredded by interstellar dust impacts at really high speeds. If you use an Orion type thing, you can bring massive heavy shielding. And it's actually not particularly crazy at all if built in space. (Actually, statistically, the real hazards of an Orion launch even from the ground would probably not be nearly as bad as your average big coal power plant. In the original Orion days they IIRC calculated 0.1-1 excess deaths per launch, but a) we could do better now, especially if the launch site was prepared right and if you don't buy the linear-no-threshold model of radiation risk, it might not affect health at all. The effects of really low radiation doses are not well known and it's debated whether they are actually harmful. The linear-no-threshold model which is used for official calculations is a conservative assumption, not necessarily right. It's completely politically unfeasible, yes, and there would probably be EMP problems as it passed through the ionosphere, but it's really not the environmental nightmare one would at first expect.) Not if you use a sun flyby. That's about right at Earth's distance from the sun. But IKAROS, at Venus' distance from the sun, got about twice that. And if you do a really close sun flyby, that can skyrocket. IKAROS is already 7.5 micrometers (0.0075mm). I don't see why future materials science, or simply less margin once we've tried them out a few times and know more about how they work in practice, couldn't reduce that.

I actually do find Minmus harder than Mun since it's easy to see when the Mun rises above the horizon, a lot harder for Minmus. Also because both times I went to Minmus I landed on crazy steep slopes.

Part of the "problem" with ions is that KSP delta-V requirements are scaled down from the real world, and LV-Ns are available in KSP. So you don't "need" ions to go anywhere in the system. Ions are useful in real life despite their thrust being more than four orders of magnitude worse than the KSP ones because: - we don't have nuclear rockets, so the next best Isp available is chemical rockets - delta V requirements are much higher - launcher size is much more limited than in KSP so you can't just bring 200 tons of fuel -you can burn constantly through the mission so low thrust is less important (you can't really do this in KSP without mods) Gigantors are much less efficient in terms of power per mass than the smaller folding panels, IIRC.

Ah -- thanks.

I tried to save with parachutes open and when I loaded they were gone and the craft plummeted to destruction. Is there a key that makes your parachute go away? Maybe I accidentally hit that while typing the save name?

The smallest solar panel and battery are massless.

Some people certainly have trouble at that altitude -- that's why passenger jet cabins (FAA rules, anyway, IIRC) aren't allowed to be depressurized below the equivalent of 8000 ft. (which is ~ 2400 m) -- but I don't think people "usually" start needing supplemental oxygen that low, at least not for short trips. Certainly I've been higher than that and not needed anything special, and I'm not super-athletic or anything. (That's about the altitude of Machu Picchu, which lots of people visit. Pikes Peak is over 4000 meters.) I think altitude tolerance is pretty variable among people though. Kerbin's atmosphere isn't actually more dense, it has the same sea level pressure at the same gravity. The game's placeholder drag model just calculates a fake "cross-sectional area" based on mass, and uses a massively too high value of 8 square meters per ton. And the atmospheric pressure does drop off faster, Kerbin's atmosphere scale height is 5 km while Earth's is 8.5 km (according to this NASA site)

Yeah, this is incredible.

I don't think it's a scam. Optimistic-leaning-toward-crazy... strike that, just plain crazy... sure. I don't actually think their ideas of how to "do" Mars are all that off base. But there's no way a reality TV show will provide enough funding to get to Mars. I doubt this. Certainly it can't be stated as an absolute. People have lived in all kinds of weird conditions without psychologists and without going crazy. If the reality TV stuff was handled wrong (too intrusive), yeah, could definitely be problematic. OTOH, anybody they would pick would have gone through probably several years of reality-TV-selection-rounds, so presumably would be good at handling that kind of environment or they wouldn't have made it that far in the first place. The point of human space exploration isn't efficiency.

Yeah. The bombardier beetle already uses a reaction involving hydrogen peroxide to produce steam... Heinlein used dragons that produce methane and ignite it in "Glory Road". As for flight... I think you'd need better power production than normal animal muscles can do. Yes, planes weighing hundreds of tons can fly just fine, but they're not wing-flappers, and they use very high energy content fuel. Pterosaurs got very big (10+ meter wingspans for Quetzalcoatlus and Hatzegopteryx... assuming they're not the same animal) but were extremely lightly built (maybe 200-250 kg???) Multi-ton dragons are trickier. I wouldn't be surprised if those big pterosaurs were pushing the limits for flying animals with conventional muscles in earth gravity and atmosphere (of course, people said the same thing about Pteranodon before they discovered Quetzalcoatlus, so...)

Orbit Manipulator Series http://forum.kerbalspaceprogram.com/threads/70881-0-23-5-Orbit-Manipulator-Series-%28WIP%29-%28Updated-March-12-2014%29 It needs Module Manager for the ion engines... But yes, this should definitely be stock... then drop the thrust by 10x or 50x...

If they are really 16x more efficient than the listed Isp, yeah, that definitely needs to be fixed. (I thought someone already pointed this out, but I can't find the post now...) The big thing there is that the Skylon is supposed to be only airbreathing up to Mach 5 (or 5.something, can't remember) which is only about 1/5 of the way to orbit (~Mach 25). But KSP orbital speeds are so much lower, and the jet engine-attainable speeds don't scale down... So KSP jet engines should probably stop working around 500 m/s or something...

I hardly think it removes choice. Personally I don't go to Minmus that often -- while Mun takes more delta-v to land on and return from, it's well within the range of rockets I'm comfortable building, and I find it easier because I can actually see the Mun rise above the horizon and thus know when to burn to get there. For Minmus I have to guesstimate it from map view. I can get to the Mun every attempt, but I have maybe a 50% (if that) success rate on getting Minmus encounters. Also, the couple of times I did land on Minmus, I ended up on really extreme slopes, which was also annoying. Minmus, yeah, gives you more science for a given delta-v, but unless you are specifically trying for that kind of efficiency, I really don't see why it matters... different playstyles, I guess.

300 million years is a long time. The farther back in time you go, the more significant of a civilization we could have missed (especially if localized to areas where we don't have fossils from that period). BUT... that doesn't mean it's at all likely. The problem remains that there's nothing for the intelligent species to evolve FROM. 300 million years ago is the end of the Carboniferous, and nothing that was alive then was doing very well in the intelligence department. That was the age of big insects, amphibians, primitive reptiles, etc. -- this lizardy thing (Archaeothyris), one of the earliest synapsids [the group including mammals and their extinct relatives], is approximately what the ancestors of mammals were like back then (OK, that's not on the direct mammal line, but still...). Nothing alive then looks at all promising as a "root stock" for intelligent life without hundreds of millions of years of evolution... which is what it took to get to us. OK, it could maybe have been faster if mammals won out instead of dinosaurs in the Triassic... but that might have cut off a hundred million years, maybe a bit more. That still means no hope for anything intelligent in the Paleozoic. Yeah, that's an interesting question. It seems like you need a lot of interacting groups, a lot of total people, for humans to really advance. But a smarter species might be able to invent a lot of stuff even in a very small local population, of maybe 1000-10000 individuals. And humans tend to expand (we colonized all the continents except Antarctica in the Paleolithic), and to take over less powerful cultures. But a species without those tendencies might conceivably develop a civilization that remained localized, despite having the technology to build oceangoing ships/airplanes/spacecraft, because they didn't WANT to travel/expand. Again, I don't think it's actually something that happened (there's no evidence, and again there's no real source for an intelligent species until quite recent times -- late Cenozoic probably), but it's an interesting thought...

Yep. As I understand it, that's what SpaceX is trying to get around by building the cheaper launch system for higher launch rates and assuming "if you build it, they will come". (Reaction Engines' Skylon project, too, but that's a lot less far along...)

I like the fact that there is way more science than you need so that you aren't pushed into visiting everything -- having "too much" science lets you choose your own path/order of doing things.

Dinitrogen tetroxide is N2O4 (a dimer of NO2, which is part of photochemical smog air pollution... N2O4/NO2 actually exist in an equilibrium depending on temperature). Otherwise correct.

Me, too. I kind of thought the "ant" engines should burn monoprop (and I think I've seen that suggested before).

This. I totally agree.

Yep. You could probably cover thousands of square miles of Nevada desert with solar panels and power California and Salt Lake City and Tucson etc., but that's a LOT of batteries. Maybe Tesla Motors will make batteries cheaper eventually... IIRC they're going to push mass production of lithium-ion batteries with a "Gigafactory".

Humans? Probably would be way too obvious, way too much evidence left. Now, you could have a "low tech"-but-ahead-of-its-time civilization we've missed -- humans were around quite a while before we have any evidence of civilization, so there could have been, say, a small local civilization on the level of say, Sumer or whatever 30,000 years ago we've missed because it existed in a place that's underwater now and didn't build big monuments out of stone that lasted. When you start going way back in geological time, it gets a bit more believable that we could miss a high-tech civilization, but even then -- if they got to our level -- our ubiquitous use of artificial materials would probably leave some sign in the fossil record. (Now maybe we've seen it already and just assumed it's natural... cool SF concept, but I doubt it.) The bigger problem for really long ago (dinosaurs etc.) civilizations is, what was the intelligent being and where did it come from? Primates have lots of species and a significant fossil record. There isn't anything like that in the Mesozoic or earlier -- the "big-brained" dinosaurs were still pretty dumb by the standards of modern birds, though larger-brained than other dinosaurs. There's a huge amount of evolution required from anything we've seen to even an ape level of brain size and complexity, much less a human one. Now, maybe you could squeeze something into the Cenozoic from a dolphin lineage or a corvid (crows/jays/etc) or parrot line, ravens and African grey parrots are apparently comparable to ape intelligence so you can imagine a sapient species coming from those lineages, but none of them has hands so... I really doubt it. (Although I've written an SF story using the concept, a Miocene marsupial species that was killed off by the freezing of Antarctica, and all that's left to find (above ice) are a few artifacts left by explorers in Argentina and the southern tip of Africa. They were bronze-age-at-best though.) IIRC in that bit "The Hunters of Pangaea" they died off because the rifting of Pangaea messed up the sauropod migration routes and killed them off, and they depended on hunting sauropods. Which is silly because continental drift is so utterly slow on the timescale of individual lives -- they would have had plenty of time to adapt, much longer than the entire existence of humanity. And we survived the extinction of our own megafauna in a much shorter period, we just learned to fish and to hunt smaller game and so on (and then to domesticate livestock and grow crops). Now, a species that was way less "exploring" than humans -- maybe one that evolved on an isolated island -- could potentially have gone extinct from local conditions. Or you could have a species that evolved just immediately before the end-Cretaceous extinction. Neither would have the chance to build a civilization, though, and both situations seem sort of a stretch to me. I don't think you need fossil fuels to develop a technological civilization. Steam engines can burn wood, and biological oils can be used as fuel, and you could probably use that to get to the point that you could develop solar or nuclear power. It likely would delay your Industrial Revolution by a century or two, as wood-burning steam engines and use of biological oils (before a Green Revolution and modern biotech) wouldn't let you do stuff on that scale, but on the grand scale a century or two isn't that much.

I would like to have a 3.75m "Hitchhiker" type habitat to do Skylab with.

True. But I would bring quite a bit more than that to allow in inefficiencies in landing and return... but not 12000, more like 8000.